Effects of n-butanol addition on the combustion and emission characteristics of a diesel engine fueled with F-T diesel and numerical simulation of soot reduction

F-T diesel and n-butanol are promising clean alternatives for diesel engines, featuring high cetane number (CN) and high octane number (ON) respectively. Blending high CN fuels with oxygenated or high ON fuels is recognized as an effective strategy to substantially mitigate soot emissions. Accordingly, the combustion and emission characteristics of F-T diesel (denoted as F100) blended with 10% and 20% n-butanol by volume (denoted as FB10 and FB20, respectively) were investigated on a diesel engine at different brake mean effective pressure ( BMEP , including 0.32, 0.64, 0.96 and 1.29 MPa) and injection timing ( IT , including 6, 10 and 14 °CA BTDC). It demonstrates that compared to F100, the brake specific fuel consumption ( BSFC ) of FB10 and FB20 rises by an average of 2.4% and 4.0%, respectively. Moreover, the minimum BSFC are observed at IT of 10 °CA and 14 °CA BTDC at low and high loads, respectively. With the addition of n-butanol, the maximum increase in brake specific NOx ( BSNOx ) for FB10 and FB20 are approximately 7.3% and 10.5%, respectively. In contrast, the reduction in soot emissions for FB10 and FB20 are roughly 24% and 44%, respectively. Subsequently, 3D simulation is further employed to investigate the kinetics mechanisms underlying the soot reduction effect of n-butanol. The results indicate that the addition of n-butanol can slightly decrease local fuel-air equivalence ratio throughout the combustion process and elevate the concentration of active free radicals (OH, O, H, and HCO). Notably, 10% n-butanol primarily suppresses soot formation by inhibiting the generation of soot precursors (A1 and C₂H₂), with a marginal promotion effect on late-stage soot oxidation, thus effectively lowering the net soot production. The study provides fundamental understanding of the combustion and soot reduction of F-T diesel and n-butanol blends, thereby offering a robust foundation for their application and utilization.